Ammonia is an intermediate compound that results from the decomposition of proteins. It is a common constituent in all domestic wastewater, as mammals eliminate most excess nitrogen via the urinary pathway. This compound is quickly hydrolyzed after leaving the body, which releases ammonia. Ammonia exists as the ammonium ion in wastewater and as the primary reduced form of inorganic nitrogen in natural water.
Pollution control statutes strive to restore and maintain the chemical, physical, and biological integrity of the public water supply. This has been accomplished through the pursuit of two goals. The first is the reduction in pollution of surface water. The second is the prohibition in discharge of toxic compounds in toxic amounts. Ammonia has been found to be toxic to forms of aquatic life at rather low concentrations. As a result, the statutes place significant emphasis on the control of ammonia in wastewater discharge.
A conventional method of wastewater treatment is the activated sludge method. A flow chart for a typical activated sludge treatment process is shown in FIG. 1. FIG. 1 shows the activated sludge process itself, without various procedures that may precede or follow the process. The activated sludge process strives maintaining a biological mass in suspension. The biological mass, or biomass, rapidly absorbs the organic (carbonaceous) material in the wastewater, which is then oxidized and used to accomplish cell growth.
The principal means of reducing the ammonia concentration in the wastewater using an activated sludge process is through the biological oxidation of ammonia to nitrate. The biomass generally contains two types of bacteria, heterotrophs and autotrophs. The heterotrophs absorb carbonaceous material and transform it into energy and cell growth. Heterotrophs have a high rate of growth. Autotrophs absorb ammonia and oxidize it into nitrates. Autotrophs have lower growth rates and cell yield, and are more temperature and pH sensitive than heterotrophs. Heterotrophs and autotrophs both prefer an environment with suitable surface area upon which to grow.
Biomass is mixed with incoming wastewater and is fed into a tank for aeration. Aeration replenishes the oxygen consumed by the activated sludge process and provides mixing to keep the biomass in suspension. In conventional systems, six hours of aeration is provided to accomplish the cell synthesis and the associated oxidation/aging for new growth. This aeration period is necessary to maintain the proper physiological state of the biomass in order to produce good separation of the biomass from the wastewater in a clarification process, resulting in a clear high quality output flow, or effluent.
The typical oxidation of ammonia to nitrate is a sequential, two step, biological process that involves two types of autotrophs. The process is outlined below.

The ammonia is oxidized to nitrite by Nitrosomas bacteria, and then is oxidized to nitrate by Nitrobacter bacteria. These two bacterial groups are autotrophs and use the ammonia as an energy source.
Heterotrophs, which use the carbon-based material as a source of energy, have a relatively high cell yield and undergo relatively rapid growth. In contrast, the autotrophs have a relatively low cell yield and relatively slow growth. The autotrophs are also more temperature and pH sensitive than the heterotrophs. Autotrophs are also strictly aerobic and require the presence of several mg/l of oxygen to achieve optimum activity.
In a conventional activated sludge process, after the aeration treatment of wastewater with biomass, biomass is separated from the flow by gravitational clarification. The net growth of biomass must be removed from the system in order to maintain proper balance between the biomass and incoming organic matter. The remainder of the biomass is returned to the influent end of the aeration process where it is mixed with incoming wastewater.
Many problems exist with the reliability of current nitrification technology in the conventional activated sludge process. If the wastewater flow is high in carbonaceous material, the growth of heterotrophs is so much greater than the growth of the autotrophs that the nitrifying bacteria are overgrown and “washed out” of the activated sludge process. This causes a substantial impairment in the ability of the conventional activated sludge process to successfully achieve reliable nitrification in a one step system.
It has been known to provide submerged media throughout the entire length of the aeration tank to act as biomass support. However these systems suffer from the same overgrowth and “wash-out” problems stated above.
Thus, in plants with a heavy carbonaceous load, nitrification cannot be undertaken effectively as an integral part of a normal activated sludge process. It is often necessary to have a separate nitrification process to treat the wastewater following the removal of the carbonaceous material. These separate nitrifying processes generally consist of a second activated sludge process employing aeration, clarification, and return sludge. Alternatively, a nitrifying filter may employ suitable surface area for the support of a nitrification biomass.
Each of these separate nitrification processes is expensive to construct and operate. A second sludge process is essentially equivalent to an activated sludge process in terms of capital investment, operation, and maintenance costs. In addition, the biomass produced is a weak, poor quality flow resulting in a poor quality effluent following clarification.
Newer nitrifying filters employ plastic media of various shapes as support for the nitrification biomass. These filters are often 20 to 30 feet deep and generally require pumping of the wastewater flow. This type of design is subject to operational problems in cold weather, as the filters are subject to icing. Other forms of fixed media, such as rotating biological contractors, have been employed in an attempt to achieve reliable nitrification. Additionally, natural sloughing of the filters results in poor quality effluent that requires additional treatment before discharge. These disadvantages represent significant capital and operating costs. A flow chart illustrating a conventional secondary nitrification treatment system is illustrated in FIG. 2.